Summary: In the mid-1980s we carried out a prospective study of early pregnancy in which we enrolled 221 health women who were planning to become pregnant. These women collected daily urine specimens for up to six months. We've assayed these specimens to describe the hormonal events of the menstrual cycle and early pregnancy. 155 women became clinically pregnant during the study, while 44 had pregnancies that ended so early that the pregnancies were detectable only by assay of urinary human chorionic gonadotropin. This unique study has been called a landmark, and continues to provide a rich resource for the description of the earliest stages of pregnancy. (More than 30,000 urine samples are still being stored.) We've published more than 40 papers from this study over the past two decades, some of which have led to new understanding of the fundamental processes of conception and early pregnancy. Last year's progress. We observed an increased frequency of intercourse during the six fertile days of the menstrual cycle among the women in our study trying to conceive. Since we could not completely rule out the possibility that intentional timing of intercourse had produced this pattern, we analyzed urinary hormones from nearly 200 additional cycles contributed by women who had been sterilized by tubal ligation or who were using intrauterine devises as birth control. We found the same pattern of increased intercourse during fertile days, confirming that the patterns are the result of natural processes and not intention. This pattern may reflect cycle effects on female libido, or on male libido mediated through female hormones. Another possibility is that intercourse may accelerate the rupture of a mature follicle and produce ovulation. Whatever the mechanism, this previously unrecognized pattern of behavior has the consequence of increasing the risk of pregnancy for a given random act of intercourse. In another project completed this year, we created glossaries of terms from reproductive epidemiology and perinatal epidemiology. These areas of epidemiology draw their terminology from diverse sources including obstetrics, sociology, and endocrinology, with considerable confusion and lack of standardization in published research reports. The purpose of these glossaries is to provide explanations for such differences, and to suggest clarifications that may help resolve apparent conflicts in the literature. Finally, we explored the question of whether human fertility has decreased over recent decades. Observations regarding an apparent decline in sperm quality have led to wide-spread discussions about possible environmental damage to human fertility. Some retrospective studies have found a decreasing fertility over time, while others have paradoxically found an increasing fertility. We carried out an extensive set of simulations to assess how this question could be addressed for recent decades. We found that concurrent changes in the availability of contraception and induced abortion are able to distort apparent fertility in unpredictable ways that make recent fertility changes nearly impossible to assess. Such changes probably explain the contradictory findings of past studies. If fertility has in fact been damaged by degradation to the environment, it is not possible to detect it at the present time.